It is known to provide a vehicle with a hydrostatic steering system. A hydrostatic steering system typically includes a gerotor pump mechanically and hydraulically connected to a steering valve, and a steering cylinder which is hydraulically connected to the steering valve. There are load reactive hydrostatic steering systems wherein the gerotor pump is hydraulically connected to the steering cylinder by the steering valve when the valve is in its center position. There are also non-load reactive hydrostatic steering systems wherein the gerotor pump is not hydraulically connected to the steering cylinder by the steering valve when the valve is in its center position. It would be desirable to provide a steering system which can easily be switched between non-load reactive and load reactive modes.
Patent application GB 2341159, published on 8 Mar. 2000 and assigned to Ognibene, shows a hydrostatic steering system with selectable reactive and non-reactive modes. However, in the Ognibene system the steering valve is an open center valve wherein, when the steering valve is in its center position, fluid flows through the steering valve to mode select valves.